In recent years, as image-recording materials, materials for forming color images have been particularly predominant and, specifically, recording materials for an inkjet system, recording materials for a thermal transfer system, recording materials for an electrophotographic system, transfer type silver halide light-sensitive materials, printing inks, and recording pens have found widespread use.
Colorants to be used in an ink composition are required to exhibit good solubility or dispersibility in a solvent, allow for high-density recording, provide a good color hue, form an image with good storage stability, be excellent in fastness to water and chemicals, have no toxicity, have high purity and, further, be available at a low cost.
That is, colorants have been improved so as to be fast to light, heat, and active gases in the environment (for example, an oxidative gas such as NOx or ozone, and SOx) by enhancing electric potential of colorant molecules (patent document 1).
On the other hand, as performance required for an ink composition, there are illustrated prevention of blurring of a colorant upon printing (patent document 5) as well as prevention of precipitation of a colorant from an ink composition or prevention of freezing of an ink composition (patent document 2), prevention of curling upon printing a substrate with an ink composition (patent document 3), and prevention of putrefaction of an ink composition (patent document 4) and, for enhancing such performance, various additives have been used in an ink composition.
As is described in patent document 6, dissolution stability of a colorant has been improved with an additive to thereby provide performance of a colorant or storage stability of an ink composition. However, it is difficult to create an ink composition which can satisfy all requirements at high levels.